Electrode arrays having a number of electrodes arranged in various patterns are used as a nerve interface for electrically stimulating a nerve or measuring a nerve action potential. To fulfill this intended purpose, the electrode array should be implanted in a living body and the wires which are bonded to the metallic (e.g. platinum) electrodes should be connected to a stimulator or measurement apparatus. As one method for enabling the multielectrode configuration of the electrode array, the technique of equipping each individual electrode with a small semiconductor chip capable of performing electrode control as well as other functions has been proposed and demonstrated (high-function electrode).
For example, in the case where the sense of sight has been lost due to dysfunction of the visual cells in the retina for converting light into electric signals (examples of the dysfunction include age-related macular degeneration and retinitis pigmentosa), while there is no problem in the ganglion cells in the retina or the optic nerves connecting the retina and the brain, the vision can be virtually restored by taking a visual image of the scene in front of the eyes using a camera or similar device and giving the ganglion cells or other remaining retinal cells two-dimensional electrical stimuli corresponding to that image. Such a system for providing a vision substitution by giving electrical stimuli to the retina is called the “artificial vision device” (for example, see Patent Literature 1).
Non Patent Literature 1 discloses a visual stimulation experiment performed on a rabbit using an artificial vision device employing suprachoroidal transretinal stimulation (STS). The measurement was performed as follows: As shown in FIGS. 1A and 1B, a flexible substrate with an array of 3×3 electrodes arranged as shown in FIG. 3 was planted in an eyeball (sclera) of a rabbit, and electrical stimuli were given to the retina from the choroid side. Meanwhile, electrodes were attached to the visual cortex on the brain of the rabbit, and the electric potential at that point (electrically evoked visual potentials) was measured.
The amount of electric current supplied to the electrodes attached to the eyeball was set at various values and the change in the brain wave was measured, with the point in time of the supply of the electric current (or stimulus) defined as the zero point. Consequently, as shown in FIG. 2, it was confirmed that the peak height (response) of the brain wave increases with an increase in the current value (stimulus). The time delay from the stimulation (approximately 20 msec) was roughly equal to the transmission delay of the vision investigated by another experiment. These facts confirm that this electrode array substrate 80 (in FIG. 3) was correctly acting as an eyeball-stimulating electrode.